When electrical characteristics of a target object such as a semiconductor wafer are inspected by using a probe card, as shown in FIG. 5 for example, tips of a plurality of probes 3A provided in the probe card 3 are imagined by a camera 2 installed at a side of the mounting table 1 for mounting thereon the target object (e.g., a wafer W) to detect the height of tips of probes 3A and electrodes of the wafer W are imagined by a separate camera to detect the height of the electrodes.
Then, the mounting table 1 is moved toward the probe card 3 based on the detected heights. The electrodes of the wafer W are made to come into contact with the probes 3A and be overdriven by a specific level, so that the electrical contacts are made therebetween under a specific contact pressure and inspection is carried out. If the contact pressure of the probes 3A is not sufficient, inspection results will be failed. If the contact pressure of the probes 3A is excessive, the probe card will be damaged.
In Japanese Patent Laid-open Application No. 2005-012119 (Reference Document 1) for example, there has been proposed a technology that after a wafer and a probe are aligned in X, Y directions, a height of tips of the probes is precisely detected to make an overdrive amount constant. In this technology, after measuring a height of a load sensor by using a laser measuring device, an ascending amount of the load sensor to come in contact with the tips of the probes is calculated, thereby obtaining a contact starting point (a height of the tips) of the probes. A height of electrodes of the wafer is measured by the laser measuring device, and the wafer is ascended, based on the difference between the height of the electrodes and the load sensor, up to the contact starting point, and then the probes are then made to come in contact with the corresponding electrodes under a constant amount of overdrive.
Further, Japanese Patent Laid-open Application No. H06-163651 (Reference Document 2) discloses a technology for detecting a contact pressure between probe needles and electrodes of a semiconductor wafer, by using a pressure sensor provided on the top surface of a wafer chuck. Until a plurality of probes are put in contact with the semiconductor wafer with a specific contact pressure, the wafer chuck ascends up to a height where the probes come in contact with corresponding electrodes of the wafer with the specific contact pressure, and inspection is performed while the wafer chuck is set to be located at the height level. As a result, the electrodes of the wafer can be put in contact with the probe needles under the specific contact pressure, thereby enhancing the reliability of the inspection.
However, recently, various types of probe cards are used, so that it becomes difficult to detect probe tips by an optical alignment method using a camera depending on materials or shapes of the probes.
The technology disclosed in Reference Document 1 is for detecting precisely a contact starting point by using a laser measuring device to set an amount of overdrive constantly and precisely, not for detecting directly a height of probe tips before an alignment of the probes. Further, the technology disclosed in Reference Document 2 is for setting a contact pressure to a specific value, not for detecting a height of probe tips upon an alignment thereof.